An advanced necklace-like metal organic framework with an ultrahighly continuous structure in the membrane for superior butanol/water separation

The fabrication of mixed matrix membranes (MMMs) for pervaporation recovery of butanol from aqueous solutions is garnering significant attention. However, constructing highly continuous metal-organic frameworks (MOFs) with reasonable loading as molecular pathways in MMMs using a scalable, mature, and controlled solution casting strategy remains challenging. We developed a novel advanced pearl necklace-like zeolitic imidazolate framework (ZIF) threaded by polypyrrole (PPy) nanotubes (ZIF-8@PPy) using a simple green approach. The inclusion of pearl necklace-like ZIF-8 throughout a PDMS matrix created micron-sized ultrahighly continuous multiple guest molecule transport channels for pervaporation separation and significantly reduced the voids and defects caused by agglomeration. For 1 wt% n-butanol aqueous solutions, the resultant MMMs with 20 wt% ZIF-8@PPy improved the separation factor from 36.4 to 70.2 while simultaneously increasing the total flux from 312.4 to 564.8 g m-2 h-1. The transport mechanism was resolved by simulation and experiments to examine the significant increase in the membrane permeability (from 31.8 to 125.2) and selectivity (from 2.3 to 4.8). The PPy nanotubes effectively inhibit the movement of water molecules and increase the fractional free volume without changing the internal regular structure of ZIF-8. The pearl necklace-like ZIF-8 with high sequence and structural integrity can be applied to prepare defect-free membranes with excellent performance for sustainable applications in petroleum, chemical, medicinal industries, or environmental protection. We also anticipate that this ultrahighly continuous MOF configuration can be extended to various other MOFs and applications.